Simian virus 40 is able to transform numerous species of cells and therefore offers an opportunity to study and characterize neoplastic transformation. Temperature-sensitive (tsA) mutants of SV40 are available which express the transformed phenotype at the permissive temperature (33 degrees C or 37 degrees C) and which shifted to the nonpermissive temperature (40.5 degrees C) assume a "more" normal phenotype. Cell cycle analysis indicates that replication of the cells at 40.5 degrees C occurs at a similar rate when compared to cells at 33 degrees C or 37 degrees C. The low saturation density at 40.5 degrees C is obtained by a balance between cellular replication and cell death. Further studies are proposed to characterize other tsA mutant transformed cells (A30 and A28) in regard to cell cycle, T antigen, integration, cell death and to further pursue the observation that a normal Chinese hamster cell monolayer will cause an arrest of cellular DNA synthesis of the tsA-transformed cell at 40.5 degrees C. With a tissue culture model of goat cells (body temperature, 40.5 degrees C), we propose to test the tumorigenicity of tsA transformed goat cells at the permissive and nonpermissive temperature in vivo. Tumorigenicity of both goat and Chinese hamster tsA transformed cells will be tested on the chorioallantoic membrane of the chicken egg at the two temperatures. These studies will define the tumorigenicity of tsA transformed cells and whether the cells, when cultured at 40.5 degrees C, are normal.